1. Field of the Invention
The present general inventive concept relates to a method of revising a medium resistance to determine a transfer voltage and an image forming device incorporating the method. More specifically, the present general inventive concept relates to a method of revising a medium resistance, to recognize a medium resistance even when an image exists within a print medium recognition interval, and an image forming device incorporating the method.
2. Description of the Related Art
Depending on a printing method that is adopted for an image forming device, the device may be categorized into a dot printing type, an inkjet printing type, and a laser printing type. Among these image forming devices, the laser printing type image forming device features a faster printing speed and a superior printing quality when compared with the dot and inkjet printing type image forming devices. These advantages have resulted in an increasing use of the laser printing type image forming device.
FIG. 1 illustrates a structure of a conventional laser printing type image forming device, and FIG. 2 illustrates a circuit formed when a voltage to recognize a print medium has been applied.
Referring to FIG. 1, the conventional laser printing type image forming device may include an organic photoconductive (OPC) drum 10, a laser scanning unit (LSU) 20, a charge roller 30, a developing roller 40, and a transfer roller 50.
The conventional laser printing type image forming device determines environment recognition conditions, such as, a low-temperature, a low-humidity environment, a normal-temperature, a normal-humidity environment, a high-temperature, and a high-humidity environment, and uses a LookUp Table charging voltage to determine a developing voltage and a (print) medium recognition voltage V.
Among them, the medium recognition voltage V is applied to the transfer roller 50 when a print medium 60 enters between the OPC drum 10 and the transfer roller 50. When the medium recognition voltage V is applied to the transfer roller 50, an electric circuit as illustrated in FIG. 2 is formed by the OPC drum 10, the print medium 60, and the transfer roller 50, and a current “i” is detected.
Typically, the conventional laser printing type image forming device is designed to set a top margin (usually, about 5 mm) of the print medium 60, and the print medium recognition is reliable only when the print medium recognition is made within the top margin of the print medium 60.
However, the print medium recognition interval is prolonged in a high speed image forming device. For instance, it normally takes 70 msec to apply the conventional print medium recognition algorithm. If the processing speed of an image forming device is 142 mm/sec, the print medium recognition interval becomes 9.94 mm (=142 mm/sec×0.07 sec), approximately 10 mm.
Since the top margin where an image is not printed on the print medium 60 is set to 5 mm, and the print medium recognition interval of the high speed image forming device may require 10 mm, an image can be printed in an interval between 5 mm and 10 mm from the top of the print medium 60.
In such case, the resistance of the print medium 60 may be increased. That is, when an image is formed within the print medium recognition interval, the current flowing through the OPC drum 10, the print medium 60, and the transfer roller 50 is decreased and the resistance is increased.
Here, because a transfer voltage applied to the transfer roller 50 is determined by the resistance of the print medium 60, if the resistance of the print medium 60 is recognized to be high, the resultant transfer voltage corresponding to the detected resistance is increased. This causes a backward transfer (paper picking or paper linting), or doubling on the top of the print medium due to a difference in the transfer voltage between the top and the area below the top of the print medium 60.
The print medium recognition voltage V is obtained by summing up a surface potential of the OPC drum 10 and the print medium recognition voltage V applied to the transfer roller 50. For example, if the print medium recognition voltage V is 1000V, then a resultant print medium recognition voltage V when no image exists on the top of the print medium 60 is 1750V (=750V+1000V), while the print medium recognition voltage V when an image exists on the top of the print medium 60 is 1150V (=150V+1000V), creating a difference of 600V.
Therefore, depending on whether an image exists within the print medium recognition interval, a difference occurs in the voltage to recognize the print medium 60 which leads to a difference in the resistance of the print medium 60, and a difference in the transfer voltage applied.
One method to resolve such an error is shortening a stabilizing time of the circuit and reducing a detection cycle by using a high-performance CPU. However, this method causes an increase in the cost of the image forming device, so it may not be adequate for a low-level image forming device as a popular model.